Diagnosis: The genus belongs in the tribe Platypodini ( Wood 1993, Alonso-Zarazaga & Lyal 2009). It is distinguished from all other Oriental genera in the tribe except Pereioplatypus Beaver, 2007, and a few species of Crossotarsus, by the presence in the male of one or two small spines or tubercles, or a carina on the anterior margin of the metaventrite-metanepisternum depression. These are reduced or absent in the female. It is distinguished from Pereioplatypus by the horizontal elytra, ending in an acute rim (obliquely declivous, and with spines at the apex of the elytral disc in Pereioplatypus). It is distinguished from Crossotarsus by the 3-segmented labial palps (2- segmented in Crossotarsus), and the anterior face of the protibia transversely carinate in both sexes (granulate in female Crossotarsus), and by the more elongate body, at least four times longer than wide (less than four times as long as wide in Crossotarsus).

Description: Small, very slender species, 2.0 to 5.0 mm long and at least four times as long as wide. Head rather prominent, wider than anterior part of pronotum, but not projecting far in front of eyes, frons nearly flat and vertical in both sexes. Eyes usually subcircular, prominent. Antenna similar in both sexes, scape short and stout, little longer than wide, funicle 4-segmented, club pubescent to base. Labial palps 3-segmented. Pronotum much longer than wide, lacking mycangial pores in both sexes, the femoral grooves more strongly angulate at their anterior end. Elytra longitudinally horizontal in both sexes, very finely sculptured, seriate punctate, declivity very short, vertical. Metaventrite-metanepisternum depression armed on anterior margin in the male by one or two small spines or tubercles, or a low carina on the metanepisternum. In the females, the tubercle or carina is reduced or absent. Abdomen obliquely raised towards apex, the male often with processes or spines on one or more ventrites. Anterior face of protibia with transverse rugae in both sexes.

Browne's (1962) diagnosis of the genus is generally accurate, but a few corrections need to be made. Browne (1962) states that the labial palps are 2-segmented, but he omits the basal palpifer from the count, and they are in fact 3-segmented as in the majority of platypodine genera ( Beaver & Sanguansub 2015). The femoral grooves are more strongly angulate at their anterior, rather than their posterior margin (contra Browne 1962), and there is a carina at the anterior angle, forming the upper margin of the femoral groove. Browne (1962) states that the abdomen is 'without abnormal modification of any of the sternites'. He may have been misled by Schedl's species descriptions, which lack any mention of the processes and spines which are often present on one or more of the first to fourth abdominal ventrites of the male. These form very useful recognition characters at specific level, and have been used extensively in the key to males (see below). Browne's (1962) suggestion that a uniform covering of moderately strong bristles, and an absence of finer hairs on the antennal club may be characteristic of the genus, is not borne out by examination of further species. Both males and females lack mycangial pores on the pronotum. Species in which the females were described with numerous pronotal pores do not belong in the genus (see below). Browne (1962) suggested that the larva of Baiocis was distinctive, but he did not describe the larva in detail in that paper, nor in his study of the larvae of old world genera of Platypodinae ( Browne 1972). The latter study only suggests that the larva closely resembles some species of Platypus. It has not been possible to examine larvae in this study.

Sexual dimorphism. There is sexual dimorphism in Baiocis, as in all platypodine genera. The dimorphism is most readily evident in the stronger sculpture of the elytral apex of the male. The lateral margins close to the male elytral apex are usually serrate, and there is a definite rim above the declivity. One or more of the ventrites in the male may be thickened or armed with processes or spines. These do not occur in the female. The last abdominal ventrite of the male is concave, but in the female convex. The spine or costa on the metanepisternum is weakly developed or absent in the female. The antennal club and eye may be slightly larger in the female than in the male.